Reducing intersystem cross talk between carrier channels



Jan. 17, 1928. 1,656,158

H. A. AFFEL REDUCING INTERSYSTEM CROSS TALK BETWEEN CARRIER CHANNELS Filed Sept. 17, 1925 [an 0 Mat "2st to East I m m w m m m Frequnuy 41am 3 m m m m m m I I H 4 2 3 1 2 Distribm'nu Jpeetb labery B AT 3 W- T T 1" r fqqqqq qq 37 East to Mst M. midst J m @2 m m m m B m m m m m m fflcw Z2 2% m m m m H 2 1 2 Jim-(2am S euth/Energy B 1 2 a 1 2 a i J i i 3 i 4 rd iq id FQ f/ INVENTOR EAL/Y/fel/ 6 ATTORNEY Patented Jan. 17, 1928.

UNITED STATES FATENT OFFICE.

HERMAN A. AFFEL, OF MAPLEXVOOD, NEXV JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

REDUCING INTERSYSTEM CROSS TALK BETWEEN CARRIER CHANNELS.

Application filed September This invention relates to multiplex transmission and more particularly to the reduction of crosstalk between multiplex carrier systems superposed on adjacent transmission systems.

In carrier transmission systems where a plurality of signaling channels are superposed upon the ordinary voice or other paling channel by the use of carrier currents ot different frequencies. crosstalk between channels on the same conductive system is prevented by the use of selecting: devices which have a range of selectivity wide enough to permit the satist'factory trans mission of all frequency components in the signal. and the various channels are spaced from each other so that a sutiicieut frequency interval exists between channels to permit the selecting devices to attain sutlicient cubott' or attenuation to prevent efl'cctivc inter -hannel crosstalk.

\Vhen two or more conductive systen'ls on the same pole line are used for carrier tran mission. another problem arises due to the rosstaili between the channcl having a given carrier trequency on one conductive system and the channel having: the same carrier trequency on an adjacent conductive system. Thi is an agr n'avateal crosstalk condition as compared with that encountered in ordinary voice transmission because the crosstalk bc cm'nes greater in magnitude as the frequency becomes higher. It has hecn proposed to reduce this type if crosstalk by so arrangthe channels that all these channels transmitting in one direction will be in one frequency range. and all those transmitting in. the opposite direction will be in another range. the channels in a given range on one transm .sion system being organized to transmit in the same direction as the corresponding channels in the same rangre in the ase of an adjacent transmission system. .Vith such an arrangement the cro stalk is 43 reduced because the transmission producim the YUI tElllI at each portion of the circu t i of the same order of magnitude as the signal t insmission in the adjacent circuit and therefor-e the induced crosstalk will be.

17, 1925. Serial NO. 57,009.

much smaller than the direct transmission. lVhile a system employing this principle is workable it' a sutticient amount of transposition and balancing work is done upon the line conductors it becomes desirable to attain further reduction in crosstalk in order to make the circuits economical. Now. the natural assumption would be, that it the channels are as closely spaced as the selective systems will permit, Without undue cross talk between adjacent channels on the same pair. the method of reducing crosstalk just de cribed would be the most effective possible. If an attempt were made. for example. to stagger the channel frequencies employed on one pair with respect to the channel trcquencies employed upon an adjacent pair it would apparently be necessary to separate the channels on each pair by the width of the signal hand in order to prevent a given channel on one pair from crosstalking on the staggered channels of the adjacent pair which lie just above and just below the first mentioned channel.

The present invention involves the dis-- covery that the channels of one system may he staggered with respect to those ot" another system. even when the channels are as closely spaced in each system as the selective devices employed will permit. without. any material tendency for a channel on one circuit to crosstalk into the channels immediately above and below it on the adjacent circuit.

The invention willnow be more fully nderstood from the following description when read in connection with the accompanying drawing Figures 1 and 3 of which are charts illu: rating two forms of channel arrangements which may be employed in accordance with the present invention. while Figs. 2 and 4 are schematic representations to indicate how the channel spacing systems of Figs. 1 and 3 respectively may be applied in cases where more than two pairs of conductors on the same pole line a multiplexed.

As already pointed out, the separation between channels in a carrier system must Slides pairs 05 conductors when more than two pairs o1" con ductors onthe same pole line are multiplexed.

Here, the frequency alliicetion shown at A in Fig. l is emplo tl for all oi the etch pair'swhile the B allocation is employer/l for all the odclpairs. By this arran 'enient the channelsot' a given pair are stag ererl with respect to the channels of the nearestatljacent pair oneacl side, while the channelsoi a given pfr will coi' ciile with the channels olf the second pair at side thereoi. Thee ce ntl pairs are net-e sariiy loc itecl at a gi1 ater distance than the immediately adjacent pairs so that the crvstall; in this case isgcuttl'o wtn in yolume by a special separationirather than' by fluency segari-ition. In other words the Q :illt between imme cli ately adjacent pair will be greatly rc clucecl by the staggering arrangeine' ts while the crosstalkbetween two systems of similar frequencyallocation wil be reduced by lack proximity, the two systems being se aratecl by an intermediate pair. I

ordinary telephone practice where phantomsare used it is, of course, customary to transpio'se ithe phantom, so that the pairs of the phantom group alternately change position. Under such conditionsthe advantages the two .difierent frequency allow-- tions may be realm-ed by assigning; different alloc jti ons to p airs having high coetiicients of cm sinduction between one another. and like a-ll ocatif to pairs having low coefli cients of cros induction between one anothen some instances staggering arrange merit e: ec irely provider! using more than two frequency E llGCSEiiOi'i S. A sys tern employing three clegr ot' staggering may be designed as indicated in Fig. 3. Here, the carrier freajnency ot' the channels numbered 1, of systems B and (7 equally spaced between the carrier frequency of channels 1 and 2 of system A. With this arrangement. thelpealts of energy in the two channels of systems B and, C fall between the peaks of energy of the two adjacent channels in system A. In thi case, ot'course, the reduction in crosstalk between any two otthe three frequencylalloczitions will not be as great as in the doubl e frequency allocationof'Fig, l. 7 On the other hanth the additionalpair combination which is made avail able by this system will, in its application t. a number of systems on the same pole line, make it possibleby stagg erin; te recluce crosstalk in cases where' one pair ifit-e'r'yenes between two circuits one crosstalk ing into theothe'r,'as well as effecting a reduction in crosstalk between two immediatel adjacent Figure 4', ofcourse" illustrates the freal ocation employed "tor the ar ous P111130!) a pole line where more the" three pairs are multiplexed. Frequency a'llo ation A used tor the and fourth pairs, frequency allocation B for the second and fifth pairs. frequency allocation C for the tlillil ana sixth airs, etc. 4

It will be obvious that. the general princii pies herein ili closecl may be einboiliecl in other and different forms withoiit departing from the spirit and scope of the appended claims. e

What is claimed is:

1. A transmission system in whicha ph rality of transmission circuits are e; 1 along the same pole line, carrier channels superposed on each transmission circuit the frequency bands of the channels on a particular circuit being only se'paratectfrbm each other by a sufficient range to prevent; undue cr sstalk from one channelto an adjacent channel on the same circuit, ancltl c frequency bands of the channels of one circuit being so allocated. with respect to the bands of the channels of the adjacent circuit that the portion of the band Carrying the maximum energy will coincide witli'the separating range between the bands of the adjacent circuit. 1 v,

2. A transmission sytem in which a plurality of transmission circuits are extended along the samepo le line a plurality of carrier channels superposed on each tranen'ns sion circuit, the frequenci' builds of the various channels of each. tra mission circuit being: separated by a frequency ran ie of Such width as to prevent undue croswata k betweena'nychannel and. an adjacent channel on the same circuit, saitl separating fr e; quency range being: oi less wiclt-h than the incliviclirelj frequency bands themselves. and the frequency bands of one transm. on circorresponding to the various channels of,

each circuit being separated from each other only by airequency range of wient with h toprevent undue croset k be 't n adjacent channels of the same ci cnit. ancl the frequency bands of the channels on any given transmission circuit being so allocated w' l: respect to the bands of other cir the same" pole line that the parts of bands carrying the maximum energy upon the two nearest adjacent circuits on each side will fall within the range separating two of the bands of the first circuit, the bands of the two adjacent circuits being also so related that the portions thereof carrying the ma: :i mum energy will be offset with respect to each other.

4. A transmission system in which a plurality of transmission circuits are extended along the same pole line, carrier channeis superposed on each transmission circuit, the frequency bands of the channels on a particular circuit being only separated from each other by a sufficient range to preventundue crosstalk from one channel to an adjacent channel on the same circuit, and the frequency bands of the channels of one circuit being so allocated with respect to the bands of the channels of the adjacent circuit that the portion of the band carrying maximum energy will coincide with a part of the bands on the adjacent circuit which corresponds to a range in which the receiving element of the adjacent circuit is incfiicient,

5. A transmission system in which a plurality of transmission circuits are extended along the same pole line, a plurality of carrier channels superposed on each transmission circuit, the frequency bands of the "arious channels of each transmission circuit being separated by a frequency range of such width as to prevent undue crosstalk between any channel and an adjacent channel on the same circuit, said separating frequency range being of less width than the individual fre quency bands themselves, and the frequency bands of one transmission circuit being so allocated with respect to those of the nearest adjacent circuit that the portion of the band carrying maximum energy will coincide with a part of the bands on the adjacent circuit which corresponds to a range in which the receiving element of the adjacent circuit is inefiicient.

6. A transmission system comprising a plurality of transmission circuits, a plurality of signaling channels superposed upon each transmission circuit, the frequency bands corresponding to the various channels of each circuit being separated from each other only by a frequency range of sufiicient width to prevent undue crosstalk between adjacent channels of the same circuit, and the frequency bands of the channels on any given transmission circuit being so allocated with respect to the bands of other circuits upon the same pole line that the portions of the bands carrying maximum energy on the two nearest adjacent circuits on each side of given circuit wili coincide with the part of the bands on the intermediate circuit which corresponds to a range in which the receiving element is inefficient, the bands of the two adjacent circuits being also so related that the portions thereof carrying maximum energy will be offset with respect to each other.

7. A transmission system in which a plurality of transmission circuits are extended along the same pole line, carrier channels superposed on each transmission circuit, the frequency bands of the channels on a particular circuit being only separated from each other by a suiiicient range to prevent undue crosstalk from one channel to an adjacent channel on the same circuit, and the frequency bands of the channels of one circuit being so allocated with respect to the bands of the channels of the adjacent circuit that the portion of the band carrying maximum energy does not coincide with the portion of the band on an adjacent circuit which carries maximum energy.

8. A transmission system in which a plurality of transmission circuits are extended along the same pole line, a plurality of carrier channels superposed on each transmission circuit, the frequency bands of the various channels of each transmission circuit being separated by a frequency range of such width as to prevent undue crosstalk between any channel and an adjacent channel on the same circuit, said separating frequency range being of less width than the individual frequency bands themselves, and the frequency bands of one transmission circuit being so allocated with respect to those of the nearest adjacent circuit that the portion of the band carrying maximum energy does not coincide with the portion of the band on an adjacent circuit which carries maximum energy.

9. A transmission system in which a plurality of transmission circuits are so related as to produce cross induction, carrier chan nels superposed upon each transmission circuit, the frequency bands of the channels of a particular circuit being only separated from each other by a sufficient range to prevent undue crosstalk from one channel to an adjacent channel on the same circuit, and the frequency bands of the channels of one circuit being so allocated with respect to the bands of the channels of a circuit having the highest coefiicient of cross induction with respect to said circuit that the portion of the band carrying the maximum energy will coincide with the separating range between the bands of said other circuit.

10. A transmission system in which a plurality of transmission circuits are so related to each other that cross induction will result, a plurality of carrier channels superposed on each transmission. circuit, the frequency bands of the various channels of each circuit being separated by a frequency range of such width as to prevent undue crosstalk on an adjacent channel of the same circuit, said separating frequency range being of less width than the individual frequency bands themselves, and the frequency bands of one transmission circuit being so allocated with respect to those. of the circuit having the 5 highest coefiicient of cross induction with respect thereto that the portion of the band carrying the maximum amount of energy will coincide with a range separating two bands on said other circuit.

In testimony whereof, I have signed my name to this specification this 16th day of September, 1925.

HERMAN A AFFEL. 

